1. Field of the Invention
The present invention relates to electrical sockets, and more particularly, is directed to an electrical socket suitable for interfacing between a printed circuit board and an electronic module, such as an integrated circuit, particularly for applications in which high-frequency signals and fast switching times are encountered.
2. Description of the Prior Art
Electrical sockets are commonplace in the electronics industry. They can be used for the temporary emplacement of an integrated circuit (IC), or other electronic module having multiple electrical leads, onto an electronic printed circuit (PC) board, or other electrical circuit. By utilizing an electrical socket, procedures such as electrical testing can be performed without the need for soldering or otherwise fixing the electronic module within the circuit. Other procedures for which the use of an electrical socket is advantageous include electrical component calibration, "burning in" active devices, and programming firmware.
In such applications, it is highly desirable that the electrical socket used be essentially "transparent" to the flow of current so that electrical signals and power transmission remain unaffected after passing through the conductive paths provided by the electrical socket. Ideally, neither the characteristics of the electronic module nor the operation of the electrical circuit should be affected by the use of a properly designed electrical socket. An electrical socket which meets the above criteria will, among other things, exhibit low electrical impedance and incorporate conductor geometry with short electrical path lengths. Otherwise, if the electrical impedance is not low, the quality of signal waveforms will deteriorate upon passing through the electrical socket. Generally, rise and fall times increase and "ringing" appears in the signal as it leaves the electrical socket. Moreover, unless conductive path lengths are negligible, signal timing problems result.
Contributing to an increased impedance in high-frequency applications is the "skin effect" phenomenon. As is well-known in the art, direct current flowing in a conductor is normally uniformly distributed throughout the cross section of the conductor. However, this does not hold for signals with alternating current (AC) characteristics. Because the effect of electrical impedance is greater near the center of a conductor than at the surface, AC signals have a tendency to concentrate near the surface of the conductor with the result that the conductor appears to the AC current to have a reduced cross-sectional area. As the effective cross section of the conductor is decreased by this effect, the resistance to AC becomes greater than the resistance to direct current. Although this problem of increased AC resistance is well-recognized in the relevant art, conventional electrical socket designs do not appear to have effectively dealt with this problem.
Timing problems may arise when an electronics module is emplaced into an electrical circuit by means of an electrical socket instead of being fixed directly into the circuit itself. Such a configuration has the effect of increasing the electrical path length for each signal passing through the conductors of the socket. These additional path lengths are usually negligible for low-frequency application, but are not negligible for circuits containing high frequency signals. Most commercially-available electrical socket designs are acceptable for low-performance applications. However, for more demanding testing incorporating faster switching times and higher signal frequencies, the inadequacy of these electrical sockets is readily apparent.
In addition to above issues related to the operation of the electronic module itself, the cost of fabricating the electrical socket itself is also a factor to be considered. As is well known in the art, an electrical socket is often custom made for a particular electronic module geometry and this usually requires the use of a separate socket for each module having a different lead configuration. Any change in the configuration of an electronic module usually requires that a different electrical socket be provided. Because electrical sockets are expensive to fabricate, each such reconfiguration incurs an additional, and undesirable, expense. Further, because of the exceptional lead time required to fabricate a custom-made electrical socket, scheduling delays result, along with their associated costs.
Typically, a design engineer or an applications technician has had a limited number of commercially-available electrical sockets from which to choose, most of which do not address the needs of the high-performance arena. To circumvent this limitation, a user often physically modifies a commercial electrical socket so as to improve its performance characteristic for a particular application. Such custom-made alterations and modifications are tedious and difficult and, once made, the modified electrical socket has limited usefulness. As the number of required components is increased for advanced applications such as complex test procedures, the number of custom-made electrical sockets required for conducting these procedures increases accordingly. The expense of providing electrical hardware and fixtures for these advanced applications grows as well. Clearly, this expense could be reduced if each additional electronic module configuration did not require a unique electrical socket. If an electrical sockets could be readily adapted for use with more than one configuration of electronic module, the expense of providing electrical hardware and fixtures could be reduced, or kept to a minimum.
The present state of the art indicates a need for an electrical socket which exhibits low electrical impedance and negligible loss of signal information when used to interface with different electronic module configurations in high-frequency applications.
It is an object of the present invention to provide an electrical socket which does not suffer from the heretofore-mentioned disadvantages and limitations.
It is a further object of the present invention to provide an electrical socket which passes signals having fast switching times without causing deterioration of the signal waveforms.
It is a further object of the present invention to provide an electrical socket having negligible signal path lengths.
It is a further object of the present invention to provide an electrical socket which can be readily adapted to accommodate more than one configuration of electronic module.